When (not if) I become famous, I will be glad to supply my publicist a video (8mm film) of me as a 3 year-old, throwing a baseball (badly), tuning a radio (loudly), and being a jerk (surely), many, many decades ago. It’s authentic as you can get.
Another way this is done is by using the actor’s earlier movies. In Whatever Happened to Baby Jane?, they showed a couple of film clips of a young Baby Jane Hudson (Bette Davis) acting to indicate she was a terrible film actress. The clips were from two of Davis’s early films Parachute Jumper (the film she hated the most) and Ex-Lady.
The Sin of Harold Diddlebock/Mad Wednesday uses footage from star Harold Lloyd’s silent film The Freshman.
Arrested Development used a joke where Michael was dating Charlize Theron. He was told she had had plastic surgery to look so beautiful, and there was a quick cut to her in her role in Monster.
Here are some of the examples I could think of offhand where they used a parent or child in a flashfoward or flashback (or something similar) scene. In The Monuments Men, George Clooney in the second to last scene (set in 1947) speaks of how he’s sure he will be proud thirty years in the future of what he did in World War II. In the last scene, his character in 1977 is touring a church where one of the art works he saved is kept. The character is played by Nick Clooney, George’s father.
In Dead Man Walking, there’s a flashback to when Sister Helen Prejean (Susan Sarandon) was a young girl, where the character is played by Eva Amurri, Sarandon’s daughter.
In Blade Runner, when the movie was re-edited the second time in 2007, twenty-five years after it was released, most of the re-editing was done just using footage shot at the time of the original filming. There were several brief shots though that require some reshooting. They got Ben Ford, Harrison Ford’s son, to play Ford’s character in those shots.
In the film Chaplin, with Robert Downey Jr in the title role, Charlie’s mother is played by Charlie’s daughter Geraldine Chaplin. Which is a nice bit of symmetry, I think, playing your actual grandmother.
Bonus trivia; Geraldine Chaplin is the mother of Oona Chaplin who played Mrs Robb Stark in Game of Thrones.
Do you know how much s movie costs? The standard Hollywood film doesn’t get made for less than tens of millions. Licensing for music and other things I’d s routine part of that process. The people funding big studio movies are already paying lawyers full time and they have standard contracts for all these things.
If you’re making a film on your own, then yeah, negotiating snd paying for licenses is time-consuming and costly.
The mugshots of a young-looking Morgan Freeman that are attached to his parole papers are actually pictures of Morgan’s younger son, Alfonso Freeman. Alfonso also had a cameo in the movie as a con shouting “Fresh fish! Fresh fish today! We’re reeling 'em in!”
In “Boston Legal” they used a number of clever tricks - including lengthy flashbacks to “Denny Crane’s” early career created from excerpts of an early William Shatner performance in “The Defenders,” and I think home movies of Candice Bergen’s youth used as memories of “Shirley Schmidt”
You’d be surprised. I used to work for a major Hollywood studio, in their interactive division. We had to pay licensing fees to the movie side of the company when we made a game based on one of their properties. Lots of money gets moved from one pocket to the other. Still comes out of your production budget.
In Jim Jarmusch’s Ghost Dog, the eponymous character is played by Forest Whitaker. In a flashback, his younger self is played by Forest’s son, Damon Whitaker, who looks a lot like his dad, minus the drooping eyelid.